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Weathering
Weathering is the break down of rocks to form sediment.
There are different types of weathering including;
CHEMICAL WEATHERING
Results in the alteration
of the chemical composition of the weathered material due to a reaction which
alters:
This is the breakdown of
rocks and minerals, which remain the same
Examples of this include Freeze / Thaw action: effect of water in cracks, freezing and expanding in volume by around 10% (in fact 9.05%) breaks the rock and Thermal/exfoliation weathering – repeated heating and cooling of rocks causes the rock to expand and contract and breakup.
BIOLOGICAL
The effect of living
things breaking up rocks
Tree roots: as a tree
grows, its roots are extended into the ground. As they grow and thicken, rocks
are prised apart. Also occurs on a slower, smaller scale by mosses and lichens.
Respiration by plant roots increases carbon dioxide in soil and assists the formation of weak acid as rainwater filters through the soil.
Burrowing animals e.g. moles, fauna break rock, and bring material to the surface
We can measure this by using a
visual measure called Rahn's Index of weathering.
This shows the various extent to which the stones have been weathered.
This is dependent on lithology (rock type), exposure and the time that the
stones have been standing.
1 Unweathered
2 Slightly Weathered - faint rounding of corners of
letters
3 Moderately Weathered - rough surfaces, letters
legible
4 Badly Weathered - letters difficult to read
5 Very badly Weathered - letters almost
indistinguishable
6 Extremely Weathered - no letters left, scaling
Find out more;
Watch this Ice wedging animation
Watch a range of animations on all different types of weathering